Air-conditioner Freezes.

[sluper]

Has anyone had their airconditioner freeze up. The Freon is not low so what could be causing the problem?

 

[B.G. Smith]

I believe in 03 they started using a thermister mounted on the face of the evapiorator to cycle the compressor off when the evaporator got to a certain temperature. It may have gone bad or become dislodged from its mounting place? bg

 

[Motorhead]

Try using your re-circulation mode. By bringing in moist outside air like I am sure you have in Ms. , moisture builds up on the cold coils. When you are on re-circ mode, you are pulling in cab air that has already been dried out by the A/C.

Does the THERMISTOR act as a switch or does it change resistance as it gets cold? Does it get higher or lower as it cools?

 

[B.G. Smith]

It is a thermal switch and opens at a predetermined temperature. bg

Try using your re-circulation mode. By bringing in moist outside air like I am sure you have in Ms. , moisture builds up on the cold coils. When you are on re-circ mode, you are pulling in cab air that has already been dried out by the A/C.

Does the THERMISTOR act as a switch or does it change resistance as it gets cold? Does it get higher or lower as it cools?

 

[sfritts]

My truck also freezes up , can you change the thermister without tearing the heater and evapiorator out?

 

[DavidC]

The thermistors I have worked on vary a voltage reading usually to a controller so that you can have the controller operate different devices at different temps. Now a Klixon which is usually a metal round device that clips onto a line is a switch that either opens or closes in a pre-determined temp. range. If you have either of these items that is the difference between the two. Just a FYI.

Dave

 

[rscurtis]

I could be wrong, but I believe the short answer is no.

 

[Motorhead]

I looked at my '07 and it looks like you could cut a small trap door into the upper cover at the back side of the evaporator (the side after the fan has blown through the evap. ) and move the thermistor either closer or farther away from the colder part of the evaporator to achieve either warmer cutout or colder cutout of the compressor. In my case, I live in a very dry climate and wish to lower the cold temperature before it cuts out the compressor. So which way would I move the thermistor?

 

[E7mack96]

if you can get to the 2 wires from the themistor, you could install a resistor and presto, temp appears different to the computer.

 

[Motorhead]

if you can get to the 2 wires from the themistor, you could install a resistor and presto, temp appears different to the computer.

OK... ... ... What value of resistor? They come in M A N Y values.

 

[E7mack96]

how many degrees would you like to change it?

 

[JJPage]

Do what you want, but I would add refrigerant, 16 oz or less.

Not sure how you determined the charge was not low, but if this just started the last couple of seasons and was fine before that, the charge is low. My 03 does this every couple of years, and a partial can of 134A always rectify's the issue.

 

[gtobey]

It is a sensor on my '06 which is pushed into the fins of the evaporator inside the hvac box. It is located to the left of where the blower motor mounts in the housing. It is a squarish place in the hvac box. The wire from that sensor comes out from between the two halves (upper and lower) and plugs into the wire harness. I was just into mine in November to fix the sorry plastic dual climate control doors, so that's how I got the pics. But I think you could cut a small hole in the box to access the thing. It is on the driver's side of the evaporator, pushed into the fins of the evaporator. Here's a picture of the wire on the front of the box to the left of the square part of the heater box containing the evaporator coils.

 

[DavidC]

So would something like this work ?

http://www.rvupgradestore.com/Thermistor-Adjuster-Dometic-p/80-8715.htm

or this

http://www.youtube.com/watch?v=SwuYp24B8Dk

Dave

 

[gtobey]

The second one may work, as it seems to be adjustable. I don't know if the one on our trucks makes connection when it freezes or breaks connection when it detects freezing conditions, like ice. You'd want to know that to match it up exactly. I think setting that to turn off the compressor when your coils freeze may prevent you from getting the most benefit from cooling, because the compressor will be going off for longer periods to correct another issue. I found when I had my A/C system discharged in order to remove the hvac box, when they serviced it by pulling a good vacuum on the system, completely removing any moisture or air, as much as possible, then properly charged it up again, it cools tremendously better! I installed a heater control valve in the heater hoses to bypass the heater core when using A/C. Now I get 39 degree air out of the center vent on high recirculate! It never did that before. The condensate water pours out of the drain, and so far, it has not frozen. I think that the other fellow was right. They will freeze if over/ u nnder charged, especially undercharged. Hope you can find the prob... It may have to be evacuated and recharged as I did to mine.

 

[RDeFayette]

go here see post #10.

http://www.dieseltruckresource.com/dev/do-remove-fin-sensor-evaporator-t245514.html

Yes they will freeze up, ESPECIALLY if the humidity is high.

1st indication is moisture coming out of the vents.

Next is complete loss of airflow.

turning the A/c off OR turning the heat on will melt the ice/blockage then it'll work again (for awhile).

Loss of airflow due to ice blockage while be a definite sign that the freon is NOT low.

Been there done that (twice).

 

[gtobey]

The relocation of the new evaporator temperature sensor with part number 5140727AA, and relocation of the new sensor to the upper right hand corner of the evaporator is meant to catch the freezing quickly. That is apparently the coldest part of the evaporator, and from other posts about dual climate controls, other folks have found out that if the Freon is low that there can be a difference in temperature in passenger to driver's side vents. The driver won't get cold and the passenger will be good. If your sensor needs replacing, I would place it where they recommend, and see how it does.



It will not matter if you turn the heater controls to hot because the evaporator is before the heater core, and not after it. None of the heat from the heater core will get to the evaporator to melt the ice as the air flows to the blower motor, across the evaporator core, then on to the heater core and then out the vents.

 

[sluper]

Thanks for all the input. I have been cycling the air off with the blower on high until the ice has melted for a while. I will check the other suggestions, as far as the high humity!! It is a hard fix down here in the South!!

 

[JJPage]

Loss of airflow due to ice blockage while be a definite sign that the freon is NOT low.

That statement is incorrect. When a refrigeration system is low on charge, temperature drops along with pressure. Pressure and temperature are relevant, when the evap temperature drops below 32*F because of low charge, it will freeze condensate on the coil and block airflow!

Thanks for all the input. I have been cycling the air off with the blower on high until the ice has melted for a while. I will check the other suggestions, as far as the high humity!! It is a hard fix down here in the South!!

Go spend $15 on a can of 134A, dump it in your system and be done with it for the season!

 

[RDeFayette]

That statement is incorrect. When a refrigeration system is low on charge, temperature drops along with pressure. Pressure and temperature are relevant, when the evap temperature drops below 32*F because of low charge, it will freeze condensate on the coil and block airflow!







Go spend $15 on a can of 134A, dump it in your system and be done with it for the season!

If the freon is low the pressure sensor will not allow the comp. to operate/cycle/etc.

Hence to ice.